Total Motorcycle Community Forums

(cut and paste from the Yahoo Radian group)

I had just finished putting in a new fuel line from my petcock to my
inline fuel filter and was taking the Rad out for a ride. All was
well for the first 50 freeway miles of the journey, but out of the
blue, it started struggling. I was doing about 55 MPH when the engine
just lost power and started sounding strange. It wasn't pinging. It
would also only do it when it had more than about 1/4 throttle
applied. It would go the same speed and make the same weird noise
from 1/4 throttle to full throttle. After riding like that for about
5 miles, it started getting worse until engine RPMs dropped below
4,000 and then all was fine - you could give it full throttle and it
would pull as strongly as always.

Any clue what this could be? I'm guessing the air filter might have
sucked something into it, I am going to pull it tomorrow morning to
see how it looks. It's an '86 Rad with 21,600 miles on it. Thanks!

Recheck to make sure you didn't kink the line ... It sounds like a carby problem right off, but i'd be leery of tearing onto the carb just yet. Is you inline filter a little clogged? Maybe when you changed your line some junk got knocked into the filter ..

Lines look fine. I just sat on the bike and rocked it back and forth and it struggled and died at idle. I'm thinking it's an issue with my vacuum petcock. I switched the line to a different carb boot and it works ok now, I guess. I'm going to replace the vacuum line and go from there.

Also, the air cleaner looked fine.

If moving the signal line to a different carb boot helped, you probably have a low-vacuum issue in that cylinder that needs checking out.

BuzZz wrote:If moving the signal line to a different carb boot helped, you probably have a low-vacuum issue in that cylinder that needs checking out.

I just balanced the carbs last week or so, they weren't too far off. :/

Moving the line changed something. Either it was crimped in the first location, or a crack opened up, that moving closed.... something. Sounds like you got it, anyway

A member of the Yahoo Rad group suggested it might be the inline filter not flowing enough. This could certainly be the problem - the filter I bought has a step-up in it. It looks like this:

---===FILTER===---

The bigger part, the ===, fits in my 1/4" ID line without a problem. I cut off the smaller diameter part on the gas tank side so it's just the larger size, but on the carb size it's still the smaller diameter. I guess I'll rip the tank off tomorrow, again, and take my trusty knife to it to fix it. Or better yet, get another filter that doesn't have the step up/down!

(edit)

Why, this fuel filter from NAPA looks to be just the ticket:

I just bought a different filter from a local auto parts store. It's of the button-style variety and seems to fit a lot better than the old, long filter. No problems with it yet, I rode my bike pretty hard a few times today and it was just fine. I also noticed a whole bunch of crap in the old filter, but it didn't seem enough to clog it.

I'll report back if it has the problem again.

Sorry to dredge this thread up, but I think I found the cause of my problems: the gas cap vent. It likes the clog and then you have a vacuum inside the gas tank, not letting any get to the carbs, making the bike run real lean. This is consistent with the symptoms I had, so I cleaned the thing out and removed some questionable parts (including a spring that decided to shoot off somewhere in the driveway ).

Hopefully this will solve it.